The present invention relates to a semiconductor device and to a method of manufacturing the same; and, more particularly, the invention relates to a technique that is effective when applied to a semiconductor device, such as a DRAM (Dynamic Random Access Memory), having a capacitive insulating film constituting an information storage capacitive element (capacitor).
The above-described DRAM is constituted of an array of memory cells, each of which has a memory cell selecting MISFET and an information storage capacitive element connected in series with this MISFET. This information storage capacitive element is formed, for example, by successively depositing silicon, so as to form a lower electrode, tantalum oxide, so as to form a capacitive insulating film, and silicon, so as to form an upper electrode.
For example, Japanese Patent Laid-Open No. Hei 5(1993)-55464 discloses a method of forming a tantalum-tungsten film 12 containing tantalum over a polycrystalline silicon film (lower electrode) 11, selectively oxidizing this film in a gas mixture of hydrogen and water vapor and forming a charge storage insulating film 14 from the resulting tantalum oxide film.
Japanese Patent Laid-Open No. Hei 7(1995)-169917 discloses a method of forming a tantalum oxide layer 5 over a high-concentration phosphorous-doped polycrystalline silicon layer (lower electrode) 3 and then crystallizing the tantalum oxide layer by first and second heat treatments. Japanese Patent Laid-Open No. Hei 7 (1995)-161934 discloses a method of forming a Ta2O5 film 5 as a capacitive insulating film over an Si-containing lower electrode (W film) 4, followed by heat treatment in an atmosphere of H2 and water vapor.
When silicon is employed for a lower electrode, however, a silicon oxide nitride film is formed on the interface between the silicon and tantalum oxide upon crystallization of tantalum oxide to be formed over the lower electrode or heat treatment (at 700xc2x0 C. in an oxygen atmosphere) of it for improving its quality, making it difficult to increase the dielectric constant.
The present inventor has carried out research and development of a DRAM and performed various investigations on the constitution and method of forming the above-described information storage capacitive element.
With the recent tendency to miniaturize a semiconductor integrated circuit device, the area of the information storage capacitive element tends to become smaller, making it difficult to maintain a desired capacitance. Therefore, it has become necessary to find electrode materials or capacitive insulating film materials that are capable of attaining a large capacitance, even if the capacitor has a small area.
The present inventor has conducted various investigations on the method of formation of an Ru film to be used as a lower electrode of an information storage capacitive element, presuming that a platinum group metal such as Ru is suited for increasing the capacitance because it does not form a film of a low dielectric constant, such as oxide nitride film, even during heat treatment, after the Ru film is formed; and, in addition, the Ru film can be formed so as to be thin, because it is a metal material.
When an Ru film is adopted as a lower electrode, however, a tantalum oxide film formed thereover tends to crack owing to volumetric expansion caused by oxidation of the Ru film upon crystallization or heat treatment (at 700xc2x0 C. in an oxygen atmosphere) for improving its film quality, resulting in a deterioration in the product yield.
Even when the volumetric expansion caused by oxidation of the Ru film is not so severe as to cause deformation of the tantalum oxide film, oxygen in the Ru film transfers even to a portion (for example, plug) of the information storage capacitive element connecting with the memory cell selecting MISFET and forms an oxide, causing conduction failure.
An object of the present invention is to provide a technique for preventing oxidation of a lower electrode due to crystallization of a capacitive insulating film or heat treatment for improving its film quality.
Another object of the invention is to provide a technique for forming a good-quality capacitive insulating film or lower electrode, thereby improving the properties of the information storage capacitive element.
The above-described objects, other objects and novel features of the present invention will be apparent from the following description and the accompanying drawings.
Of the aspects and features of the invention disclosed in the present application, representative ones will be described briefly below.
1. A method of manufacturing a semiconductor device according to one aspect of the present invention comprises (a) forming a first conductor over a semiconductor substrate, (b) forming a first insulating film over said first conductor, and (c) after said step (b), heat treating said semiconductor substrate in an atmosphere containing water and hydrogen.
2. A method of manufacturing a semiconductor device according to another aspect of the present invention comprises (a) forming a first conductor over a semiconductor substrate, (b) forming a first insulating film over said first conductor and (c) heat treating said semiconductor substrate at 200 to 400xc2x0 C. in an atmosphere containing water and hydrogen.